Particle Physics: BaBar Data Hint at Cracks in the Standard Model

ScienceDaily (June 18, 2012) — Recently analyzed data from the BaBar experiment may suggest possible flaws in the Standard Model of particle physics, the reigning description of how the universe works on subatomic scales. The data from BaBar, a high-energy physics experiment based at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory, show that a particular type of particle decay called "B to D-star-tau-nu" happens more often than the Standard Model says it should.

In this type of decay, a particle called the B-bar meson decays into a D meson, an antineutrino and a tau lepton. While the level of certainty of the excess (3.4 sigma in statistical language) is not enough to claim a break from the Standard Model, the results are a potential sign of something amiss and are likely to impact existing theories, including those attempting to deduce the properties of Higgs bosons.

"The excess over the Standard Model prediction is exciting," said BaBar spokesperson Michael Roney, professor at the University of Victoria in Canada. The results are significantly more sensitive than previously published studies of these decays, said Roney. "But before we can claim an actual discovery, other experiments have to replicate it and rule out the possibility this isn't just an unlikely statistical fluctuation."

The BaBar experiment, which collected particle collision data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. The collaboration's data helped confirm a matter-antimatter theory for which two researchers won the 2008 Nobel Prize in Physics.

Researchers continue to apply BaBar data to a variety of questions in particle physics. The data, for instance, has raised more questions about Higgs bosons, which arise from the mechanism thought to give fundamental particles their mass. Higgs bosons are predicted to interact more strongly with heavier particles -- such as the B mesons, D mesons and tau leptons in the BaBar study -- than with lighter ones, but the Higgs posited by the Standard Model can't be involved in this decay.

"If the excess decays shown are confirmed, it will be exciting to figure out what is causing it," said BaBar physics coordinator Abner Soffer, associate professor at Tel Aviv University. Other theories involving new physics are waiting in the wings, but the BaBar results already rule out one important model called the "Two Higgs Doublet Model."

"We hope our results will stimulate theoretical discussion about just what the data are telling us about new physics," added Soffer.

The researchers also hope their colleagues in the Belle collaboration, which studies the same types of particle collisions, see something similar, said Roney. "If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model."

The results have been presented at the 10th annual Flavor Physics and Charge-Parity Violation Conference in Hefei, China, and submitted for publication in the journal Physical Review Letters. The paper is available on arXiv in preprint form.

This work is supported by DOE and NSF (USA), STFC (United Kingdom), NSERC (Canada), CEA and CNRS-IN2P3 (France), BMBF and DFG (Germany), INFN (Italy), FOM (The Netherlands), NFR (Norway), MES (Russia), and MICIIN (Spain), as well as support from Israel and India. Individuals have received funding from the Marie Curie EIF (European Union) and the A.P. Sloan Foundation (USA).

Source: http://www.sciencedaily.com/releases/2012/06/120618111823.htm

LED Measurement System

As we know, there are many light sources which can be used for lighting system. In the past, when the electricity hasn’t been used for lighting technology, candle and torch were used for it. Thomas Alfa Edison started lighting technology by his invention, incandescent lamp. Then, fluorescent lamp technology has been being used. Now, the development of LED light has begun to replace fluorescent lamp and other light source. LED is light source whose its efficiency is very high because it converts directly from electricity to light.

As a light source, LED has properties as other light source, such as: Flux Luminous, Intensity, Luminance, Radiance Flux, etc. Measuring these properties needs instrument or equipment. The development instrument technology makes the measurement of Light properties (especially LED light properties) become easier. To measure LED light properties need at least spectrometer, integrating sphere, fiber optic, and software. Several companies has developed this kind of instrument in one system.

Spectrometer

Spectrometer is equipments that analyzed the wavelength of light. Light that comes to spectrometer will be refracted by prism or grating, so light will be separated based on its wavelength. This wavelength will be analyzed by CCD to be converted into electric signal.

Fiber optic

Fiber optic is used to be path of light. Fiber optic is put in front of light source, so light can enter to the fiber optic and go to spectrometer to be analyzed

.

Integrating Sphere

Integrating sphere is a hollow sphere which is coated by white color. The function of integrating sphere is to collect 

all of light emitted by light source.

PC and software

Electric signals from spectrometer are the information of light. To know what signal said, it needs process to be understood. This process is done by computer with compatible software. Spectrometer is usually completed by its software.

LED Junction temperature measurement using forward voltage method

LED performance highly dependence to junction temperature. Therefore, LED junction temperature is one of the important parameter in LED. Until now, there are two kinds of measurement method which can be used for determining LED Junction temperature, Forward voltage method and Shift wavelength method. This article will discuss about LED junction measurement temperature using forward voltage method.

Forward voltage method based on the temperature dependence of diode forward voltage. Since LED is diode, this dependence also occurs at LED. The simple explanation of this dependence is the difference temperature will result different forward voltage, although current flows are same. For example, let’s say LED junction temperature is 20 Celsius and current is 20 mA, the forward voltage 2 Volt. Then when the junction temperature increase, let’s say 40 Celsius, the forward voltage will decrease, may be 1.96 volt. This kind of relation can be used for determining junction temperature.

This method contains two steps, calibration measurement and actual measurement. The function of calibration measurement is to get the reference data. For calibration measurement, we need several equipments: oven, pulse generator, oscilloscope, thermocouple, resistor (if using pulse voltage generator).

LED is put and heated inside oven until certain temperature. Then it is injected by pulsed current using pulse generator. The current must be same with the operating current of the LED. Then, measure forward voltage of LED. This measurement is repeated again with different temperature by increasing set point temperature of oven. It can be done by choosing several temperatures, such as: 20, 40, 60,..,120 Celsius. By this way we will get the relation between temperature and forward voltage.

There are several important things that we have to consider:

1.        Duty cycle from pulse generator must be very low, such as 0.1%. By using very low duty cycle, so heat dissipated from LED can be neglected, thus oven temperature can be assumed is same with LED Junction temperature. Finally, we can establish relation between Junction temperature and forward voltage.
2.    Thermocouple is used to make sure the oven temperature. Thermocouple must be put close to the LED. 
3. To make sure that LED temperature is same with oven temperature, LED must be waited inside oven for while after oven has achieved set point temperature. It can be 30 minutes or longer. 
4. If there are differences between set point temperature and temperature shown by thermocouple, so choose the temperature which is shown by thermocouple. It is because thermocouple is put close to LED, while temperature sensor at oven system may be at the other place.

The data from calibration measurement can be drawn as a graph. This graph is usually very linear. We can do the linear regression.

Next step is actual measurement. At this measurement, LED is put at the operating place and supplied by operating current. It may be DC current. When the LED is supplied by DC current, its voltage will decrease and achieve stable condition after a while. So, at this measurement, LED must be waited until it achieves stable condition. Approximately it will take 2 minutes. After that we can measure the forward voltage of LED by voltmeter or multimeter.

This forward voltage can be used to determine junction temperature measurement. Data from calibration measurement is used as reference. For example, the voltage from actual measurement is 1.7 Volt. Then, we can search what temperature shown when the forward voltage is 1.7 Volt.

Spectrometer

Light is kind of electromagnetic wave. Visible light for example, this is an electromagnetic wave which has wavelength that can be sensed by human eye. Source of light may emit light not only one wavelength. White light consist many wavelength from 380 nm – 750 nm. The proof about this is when white light (such as sun light) is refracted by prism, we can see many color (from red to violet) as a result. Color of light depends on the wavelength, so we can conclude that sunlight consist many wavelength.

Spectrometer is an instrument which can be used for measure light properties. The variable can be measured by spectrometer usually is intensity. Electronic spectrometer consists of device which can convert from light to electricity, it is called CCD.

The steps inside electronic-spectrometer are started with light enter the spectrometer, then a device (Prism or grating) refracts the light based on its wavelength. For example white light will be refracted into all of visible light wavelength. These wavelengths will be converted into electric signal by CCD. This signal will be transmitted to PC to be processed. Finally we can see the spectrum of light on the PC’s monitor. Usually electronic spectrometer is completed with its software which can be used to measure in several units, such as Watt, Lumen, Lux, etc.

Spectrometer is used for many applications, Such as solution identification and LED Junction temperature Measurement.